1. Field of the Invention
The present invention relates to a position detector for a moving vehicle, and more particularly to a position detector for traveling a moving automobile, an unmanned mobile and carrying device in a factory, or a steering vehicle for use in agriculture, civil engineering machinery and the like along a predetermined traveling course.
2. Description of the Prior Art
Heretofore, as a system for detecting a present position of a moving body such as the moving vehicles as described above, there has been proposed a system provided with a means for scanning light beam emitted from a moving body in the circumferential direction or every azimuthal directions centering around the moving body, light-reflecting means for reflecting to return the light beam in the direction of incident light and positioned at least three positions apart from the moving body, and a beam receiver means for receiving light reflected from the light-reflecting means (the Japanese Patent Laid-open No. 67476/1984).
In the above mentioned prior art, differential azimuthes between adjoining two of three light-reflecting means centering around the moving body are detected on the basis of received beam output of the light-receiving means, then a position of the moving body is operated based on the detected differential azimuthes and positional information of the light-reflecting means which have been previously set.
Also, the present inventors proposed in U.S. Ser. No. 344,574 a control system which, different from the above described system wherein the positional informations of the light-reflecting means are preset, detects the distances between a moving body or a moving vehicle and the light-reflecting means and, based on the detected distances and the differential azimuthes, operates the positions of the light-reflecting means thereby to detect the position of the moving vehicle.
In that control system, if there are some unexpected light-reflecting objects other than the expected light-reflecting means in the neighborhood of the area in which the moving vehicle travels, the light-receiving means may receive the light reflected from the unexpected light-reflecting objects. For this, the present inventors proposed in U.S. Ser. No. 413,934, an improved control system which predicts the azimuth at which light-reflecting means is to be detected in the next scan, based on the azimuth (the angle formed between the advance direction of the moving vehicle and the direction of the light-reflecting means) at which the light-reflecting means has been detected the current and last scans, and determines that the light incident upon the light-receiving means within the predicted azimuth is the normal reflected light from the expected light-reflecting means. However, in that control system, if the difference between the azimuth of the expected light-reflecting means as viewed from the moving vehicle and the azimurth of other reflecting object is large, both can be discriminated from each other, whereas there are cases that they can not be discriminated and the normal light-reflecting means can not be detected if the azimuthes of the two were close to each other and the both of two are included in a predicted angle range.
That is, since the predicted azimuth has a predetermined detection range there is a problem that if the azimuthes of the expected light-reflecting means and the unexpected reflecting object are close to each other, the reflected lights from the two are naturally detected in the predetermined detection range.
If a plurality of incident lights are received in the detection range as mentioned above, the distance between the source of each incident lights and the moving vehicle is measured, the source which is nearest to the moving vehicle is determined to be the expected light-reflecting means, and based on the azimuth of this light-reflecting means, the position of the moving vehicle can be detected (Japanese Patent Application Serial No. 46407/1989). The above mentioned detection method requires the assumption that obstacles such as unexpected reflecting objects existing in the limited range such as the area in which the moving vehicle travels have been removed before the work is begun, and it has an advantage that, in practice, the above-mentioned problem can be removed by a simple control system.
In the above described prior art, measurement of the distance between the moving vehicle and the light-reflecting means is performed on the basis of the phase difference between the light beam generated in the light beam emitting means mounted on the moving vehicle and the incident light reflected by the light-reflecting means or other light-reflecting object.
In this method, since the light-receiving level varies if the distance between the moving vehicle and the light-reflecting means or other unexpected reflecting object differs, time is required for level matching of the light beam generated at the light beam emitting means and the incident light for detecting the phase difference. Also, time is required for the operation of the distance and the like. Therefore, if the scanning speed of the light-receiving means is made slow so that the time from the reception of one incident light to the reception of the next incident light is set as long as possible, it is convenient for adjustment of the incident light level and distance operation, etc.
On the other hand, however, there is a problem that, if the rotational speeds of the light beam emitting means and light-receiving means for scanning is slow with respect to traveling speed of the moving vehicle, time difference of azimuth detection occurs between each light-reflecting means or objects, whereby the precision of positional detection is reduced. There is requirement to increase the number of revolutions of the light beam emitting means and light-receiving means (the rotational speed of the light beam scanning means) in order to reduce the time difference in the azimuth detection.
As described above, there is a problem that the two requirements incompatible with each other must be fulfilled in order to improve the prior art.